Mixed indicator composition



Patented Dec. 22, .1953 it Inc NiiwiYb'i'kQfNI acornoratioh'iofthelawareNo,.Dra.wingg pplicationfieptember :2;:,-1,949,m

s Serial .No. 11'3,888

'Tlie presentinvention isdirectedto' composi= tions adapted to indicatea change of'pI-Ijarfd more particularly to an indicator adaptedfor-determinirrg" the alkalinity" of various. solutions.

FO'I a considerame number f years 'n'lfitfiyl' f orange has been'used'as ari'indicatorintitrating alkalinesolutions -whier einirlthe"originalx r-yello'vv color of the indicator chang e' tc'e'reu:ink-passing from alkal'iiie to aciii condition.--=The coler transt tion1 took-place over a" relativel-y -v. ide- 'range" of pH? sayyfromfifl toi. The-change was-grad ual and not 'sufliciently accurate for many pu a:poses as the end p'oint was not sharply defined. In certairr cases wherethe alkalinity of such water asis used forboiler feed and contains somecolor, the end point was further masked and the inaccuracy accentuated?In order to a-overcome -zthesein defe'ctseu various changes in theindicator itself ha ver=beerisug+ gested 'but :none:of them-have'satisiactorihgovercome the deficienciesi one such .proposaluwastoprovide a miX ture" ofi meth'yli' orange "tlie formpf its sodium saltwith alphaz'ur'inei water solution. The added blue dye made-tha endpoint somewhat: more easily deteetabl e but it changed -theen-d poin tto a difirent pl l whicli may beundesirable in titrating of 'a1lali-r'iity--of: boiler 'feed-:waters;" Furthermore-,2-the clrange at theend l point is*- over I a considera'blrangeas the color changes fromgreen -'-tcgreen 'grayto purple-gray to purple during the transition,and such transition is not sufiiciently sharp, particularly as thegreen-gray is usually taken as the end point.

The present invention is intended and adapted to overcome thedifficulties and disadvantages inherent in prior indicator compositionsfor the purpose described, it being among the objects of the presentinvention to provide an indicator composition which is capable of givingan end point which is sharp and accurate and wherein the transition isover a very short range of pH.

It is also among the objects of the present invention to provide anindicator composition which is particularly suitable for use intitrating alkaline boiler feed waters for the purpose of determining theamount and character of addition agents for treatment of said water.

It is further among the objects of the present invention to provide anindicator composition in solution in water which is stable over longperiods of time and which is not adversely affected by impurities in thewater being tested.

Essentially the invention is based upon the provision of a mixture ofdyes or indicators and s oiainas. (c1. zsz m's-rsnecific'allyltliereiares-pripvided ithree 'isuc'ii dyfesi The;principal compound is" ethyl orange; which constitutes. the.majorinonstituenti' The'amount .within' a very;narrow'frange'goffpH..'The" sharp-i ness. and accuracy, is present" evlenjt though "thewatermay be relatively liighlyicolor d More specifically thereis'"ad'dedto'"tli'e ethyl orange a mixturenoi alphazurineA andjfuch'sin"ingabout'onethird'oftheamountlof alphazurin l Siiclioompositions;operatewithinth.rangefiof.pHbetween 3.8 land '.4.0.-.. v h

,To provideltliadsir'edjdomposition, there is dissolved 'inll 10190oo...oflwateratheimixture of ffconstituents in.therfolldw-ingaproportions I H Grams: Ethyl orange .2;Oito.. 2.5'Alphazurifie mnn L-1;4 to 1&6

The amount 'of "in'di'catoryaries froni 318"to 4.7"

Grams per liter Ethyl orange 2.33 Alphazurine A 1.50 Fuchsin red 0.50

When this indicator is added to an alkaline solution it provides areadily distinguishable, clear, green color. As titration proceeds, thegreen changes to a gray at a pH of 4.2 to 4.3. This constitutes awarning to the chemist that he is approaching the end point andtherefore he pays close attention to the changes. Then at a pH of 3.9 to3.8 the gray changes to a bright purple by the addition of a single dropof a standard acid solution normally used for the purpose. In this way,a very accurate titration is obtained.

The ethyl orange used in the composition is the 4-diethylaminoazobenzene sulionic acid. The alphazurine A is the calcium salt of thedisulionic acid of m-hydroxy-dibenzyldiethyldiamino-triphenyl-carbinol.The fuchsin red is a mixture of pararosaniline (triamino triphenylcarbinol) and rosaniline (triamino-diphenyltolyl-carbinol)-hydrochlorides.

Although the invention has been described setting forth a singlespecific composition, the invention is not limited thereto as slightchanges in the proportions of the several dyes named herein within thelimits set forth may be made with good results. By such changesdesirable variations in the end point within the specified range may beobtained. The presence of small amounts of inert constituents other thandyes, does not adversely affect the indicator. Dyes which are theequivalent of those specifically named may be used in part or in wholefor the same. The fuchsin red is a mixture of two substances on whichthe proportions may vary, but generally it is convenient and prferableto use color index No. 677, which is a standard in the dye industry. Itis not essential that the hydrochlorides of the rosaniline dyes be used,but other salts, for instance, acetates, are equally suitable. Theindicator of the present invention is applicable wherever methyl orangeis used and in other titrations than boiler feed waters. By theexpression boiler feed waters there is included boiler and similarwaters as well as the feed waters for boilers and the like.

These and other changes in the details of the invention may be madewithin the spirit thereof and the invention is to be broadly construedand not to be limited except bythe character of the claims appendedhereto.

We claim:

1. A composition for indicating color changes in titration consistingessentially of a mixture of ethyl orange, alphazurine A and fuchsin red,the ratio of alphazurine to fuchsin being about 3 to 1, dissolved inwater in the amount of 3.8 to 4.7 grams per liter the ethyl orange beingin an amount about equal to the sum of the amounts or the other dyespresent, the color thereof being green and changing to gray-purple inthe range of pH 4.3 to 3.8. r

2. A composition for indicating color changes in titration consistingessentially of a mixture of ethyl orange, alphazurine A and fuchsin red,the

Grams Ethyl orange 2.0 to 2.5 Alphazurine A 1.4 to 1.6 Fuchsin red 0.4to 0.6

4. A composition for indicating color changes in titration consistingessentially of a mixture of ethyl orange, alphazurine A and fuchsin red,dissolved in water in the amount of 3.8 to 4.7 grams per liter, thecolors being in the following proportions:

Grams Ethyl orange 2.33 Alphazurine A 1.50 Fuchsin red 0.50

5. A composition for indicating color changes in titration consistingessentially of a mixture of ethyl orange, alphazurine A and fuchsin red,the ratio of alphazurine to fuchsin being about 3 to 1, dissolved inwater in the amount of 3.8 to 4.7 grams per liter, and having an endpoint at a pH of 3.8 to 4.3 with a purple color.

JOSEPH V. CORSO. RICHARD C. ULMER.

References Cited in the file of this patent Prideaux J.: Soc. Chem. Ind,vol. 45, pp. 664, 678, 697 (1926).

Kolthofi et al.: Acid-Base' Indicators; The Macmillan Co., New York,1937, pp. 172-177.

Britton: Hydrogen Ions, vol. I, 3rd ed., D. Van

Nostrand Co., Inc., New York, N. Y. (1943), pp.

1. A COMPOSITION FOR INDICATING COLOR CHANGES IN TITRATION CONSISTINGESSENTIALLY OF A MIXTURE OF ETHYL ORANGE, ALPHAZURINE A AND FUCHSIN RED,THE RATIO OF ALIPHAZURINE TO FUCHSIN BEING ABOUT 3 TO 1, DISSOLVED INWATER IN THE AMOUNT OF 3.8 TO 4.7 GREAMS PER LITER THE ETHYL ORANGEBEING IN AN AMOUNT ABOUT EQUAL TO THE SUM OF THE AMOUNTS OF THE OTHERDYES PRESENT, THE COLOR THEREOF BEING GREEN AND CHANGING TO GRAY-PURPLEIN THE RANGE OF PH 4.3 TO 3.8.